Since cardiomyocytes lose their division potential at the time of birth and hence their regeneration is difficult, recent interest has focused on replacement therapy wherein cardiomyocytes obtained by differentiation induction of cells having pluripotency (WO 2007/069666), such as embryonic stem cells (ES cells) and induced pluripotent stem cells (iPS cells), are transplanted to a cardiac tissue damaged due to myocardial infarction, myocarditis, aging or the like. Although many methods for differentiation induction of such pluripotent stem cells into cardiomyocytes have been reported (WO2007/002136, WO2009/118928 and Yan P, et al, Biochem Biophys Res Commun. 379:115-20 (2009)), there are only a small number of reports which mention proliferation of the induced cardiomyocytes. For example, as methods aiming to regenerate cardiomyocytes themselves, a method wherein nuclear-localized cyclin D1 and CDK4 are expressed to promote proliferation of cardiomyocytes (WO2005/049822) and a method using a p38 inhibitor (Engel F B, et al, Proc Natl Acad Sci USA. 103:15546-51 (2006)) have been reported.